In the fabrication of semiconductor integrated circuits (ICs) it is typical, at an early stage in the fabrication process, to form isolation regions that provide electrical isolation between various parts of the circuit. One such isolation region is the shallow trench isolation (STI). STI is basically a trench etched into the surface of a semiconductor substrate in the location where isolation is needed that is filled with an insulating material such as a silicon oxide.
As ICs become more complex and incorporate more and more devices it becomes necessary to reduce device size. Reducing device size also implies that the width of STI trenches must be reduced. Reliably filling STI trenches is difficult when the minimum feature size, that is the minimum line width and spacing used in designing a device, decreases to 40 nanometers (nm) or even less. Conventional oxide filling using, for example, low pressure chemical vapor deposition (LPCVD) or high density plasma chemical vapor deposition (HDP) is ineffective. Such techniques cannot reliably fill high aspect ratio trenches. Other materials and processes such as spin-on-glasses have been developed to fill high aspect ratio trenches but such fill materials tend to be soft and thus sensitive to etchants used during etching steps and to cleaning agents, especially those containing hydrofluoric acid, that are used in subsequent processes. Loss of fill material from the STI results in a non-uniform topography which, in turn, causes yield limiting process problems. The loss of fill material also causes undesirable device performance variations.
Accordingly, it is desirable to provide high yielding methods for fabricating semiconductor integrated circuits having reduced STI fill loss. In addition, it is desirable to provide methods for fabricating semiconductor ICs having hardened shallow trench isolation fill. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.